MongoDB学习笔记(查询)

1. 基本查询：

构造查询数据。

> db.test.findOne()

{

"_id" : ObjectId("4fd58ecbb9ac507e96276f1a"),

"name" : "stephen",

"age" : 35,

"genda" : "male",

"email" : "stephen@hotmail.com"

}

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--多条件查询。下面的示例等同于SQL语句的where name = "stephen" and age = 35

> db.test.find({"name":"stephen","age":35})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35, "genda" : "male", "email" : "stephen@hotmail.com" }

--返回指定的文档键值对。下面的示例将只是返回name和age键值对。

> db.test.find({}, {"name":1,"age":1})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35 }

--指定不返回的文档键值对。下面的示例将返回除name之外的所有键值对。

> db.test.find({}, {"name":0})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "age" : 35, "genda" : "male", "email" : "stephen@hotmail.com" }

2. 查询条件：

MongoDB提供了一组比较操作符：$lt/$lte/$gt/$gte/$ne，依次等价于/>=/!=。

--下面的示例返回符合条件age >= 18 && age <= 40的文档。

> db.test.find({"age":{"$gte":18, "$lte":40}})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

--下面的示例返回条件符合name != "stephen1"

> db.test.find({"name":{"$ne":"stephen1"}})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

--$in等同于SQL中的in，下面的示例等同于SQL中的in ("stephen","stephen1")

> db.test.find({"name":{"$in":["stephen","stephen1"]}})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

--和SQL不同的是，MongoDB的in list中的数据可以是不同类型。这种情况可用于不同类型的别名场景。

> db.test.find({"name":{"$in":["stephen",123]}})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

--$nin等同于SQL中的not in，同时也是$in的取反。如：

> db.test.find({"name":{"$nin":["stephen2","stephen1"]}})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

--$or等同于SQL中的or，$or所针对的条件被放到一个数组中，每个数组元素表示or的一个条件。

--下面的示例等同于name = "stephen1" or age = 35

> db.test.find({"$or": [{"name":"stephen1"}, {"age":35}]})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

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--下面的示例演示了如何混合使用$or和$in。

> db.test.find({"$or": [{"name":{"$in":["stephen","stephen1"]}}, {"age":36}]})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

--$not表示取反，等同于SQL中的not。

> db.test.find({"name": {"$not": {"$in":["stephen2","stephen1"]}}})

{ "_id" : ObjectId("4fd58ecbb9ac507e96276f1a"), "name" : "stephen", "age" : 35,"genda" : "male", "email" : "stephen@hotmail.com" }

3. null数据类型的查询：

--在进行值为null数据的查询时，所有值为null，以及不包含指定键的文档均会被检索出来。

> db.test.find({"x":null})

{ "_id" : ObjectId("4fd59d30b9ac507e96276f1b"), "x" : null }

{ "_id" : ObjectId("4fd59d49b9ac507e96276f1c"), "y" : 1 }